1. Technical Field
The present disclosure relates to a method of preparing a catalyst having polymer electrolyte multilayers containing dispersed (inserted or attached) Pt—Pd particles as a metal component, suitable for use in production of hydrogen peroxide. More particularly, the present disclosure relates to a method of preparing a catalyst having Pt—Pd loaded polymer electrolyte multilayers for use in the production of hydrogen peroxide, wherein polymer electrolyte multilayers are formed on an anionic resin support, treated with sulfuric acid and then loaded with Pt—Pd particles, thereby maintaining high activity for a long period of time, and to a method of directly producing hydrogen peroxide from hydrogen and oxygen using a catalyst prepared by the above method.
2. Description of the Related Art
Hydrogen peroxide is weakly acidic and is a colorless liquid miscible with water, and is thus widely utilized as an oxidant, a bleaching agent, etc. Typically useful for the production of hydrogen peroxide is an anthraquinone process, by which 95% or more of the total supply of hydrogen peroxide is produced, as is currently known. An anthraquinone process is carried out via cyclic reaction of hydrogenation of anthraquinone and oxidation as illustrated below.                Hydrogenation (reaction between hydrogen and anthraquinone (Q) to produce anthrahydroquinone (H2Q))        
                Oxidation (oxidation of anthrahydroquinone (H2Q) to produce H2O2)        

In addition thereto, filtration, extraction of hydrogen peroxide and the like are involved between the hydrogenation and the oxidation.
As mentioned above, anthraquinone acts as a carrier, so that oxygen and hydrogen do not come into direct contact with each other. For example, the modified technique of the above process is disclosed in U.S. Patent Application Publication No. 2009/291844, wherein hydrogen peroxide is formed from water and oxygen by cyclic reaction of quinine-hydroquinone in the presence of applied voltage.
However, an anthraquinone process involves a plurality of reactions wherein byproducts are formed by side-reactions through individual steps, thus requiring regeneration of the anthraquinone solution and separation and refining of hydrogen peroxide from the anthraquinone solution [J. M. Campos-Martin, G. Blanco-Brieva, J. L. G. Fierro, Angew. Chem. Int. Ed., vol. 45, pp. 6962 (2006)]. Accordingly, the production of hydrogen peroxide by the anthraquinone process needs high energy and processing costs, undesirably decreasing price competitiveness of hydrogen peroxide.
With the goal of solving the problems with the anthraquinone process, research into direct production of hydrogen peroxide from oxygen and hydrogen without formation of byproducts other than water is ongoing (Liu et al., Angew Chem. Int. Ed., 2008, 47, 6221-6224).
However, this method has the following problems: First, a mixture of oxygen and hydrogen has a high risk of explosion due to a very wide explosion range depending on the mixing ratio thereof. When the concentration of hydrogen in air at 1 atm is 4 to 75 mol %, explosion may occur by an ignition source, and when oxygen is used instead of air, the explosive hydrogen concentration may be further widened to 4 to 94 mol %. As the pressure is higher, such a concentration range may become wider, and thus, the explosion potential may also increase (C. Samanta, V. R. Choudhary, Catal. Commun., vol. 8, pp. 73 (2007)). Upon direct production of hydrogen peroxide using hydrogen and oxygen reactants, the mixing ratio of hydrogen and oxygen may be adjusted in the safe range, and an inert gas such as nitrogen or carbon dioxide may be used to lower the concentration of hydrogen and oxygen. Second, even when hydrogen peroxide, which is very unstable, is produced, it may be easily decomposed into water and oxygen, and a catalyst useful for production of hydrogen peroxide may also become efficient for synthesis of water, making it difficult to obtain high hydrogen peroxide selectivity. As for the production of hydrogen peroxide from oxygen and hydrogen, high-activity catalysts and strong acid and halide additives are under study to solve the above problems.
In this regard, direct production of hydrogen peroxide from hydrogen and oxygen using a catalyst obtained by loading a precious metal on any support such as alumina, silica or carbon has been developed (V. R. Choudhary, C. Samanta, T. V. Choudhary, Appl. Catal. A, vol. 308, pp. 128 (2006)). In order to increase hydrogen peroxide selectivity, the addition of an acid to a solvent to inhibit decomposition of hydrogen peroxide, and the addition of halogen ions to a solvent or catalyst to prevent the formation of water from oxygen and hydrogen are known (Y.-F. Han, J. H. Lunsford, Catal. Lett., vol. 99, pp. 13 (2005); Y.-F. Han, J. H. Lunsford, J. Catal., vol. 230, pp. 313 (2005); WO 2001/5501). Although an additive such as acid or halogen ions may function to increase hydrogen peroxide selectivity, it may cause corrosion problems or may dissolve out the metal such as Pd loaded on a support, undesirably deteriorating the activity of the catalyst and requiring separation and refining after production of hydrogen peroxide. Hence, the use of such an additive may be suppressed if possible.
The present applicant proposed a method of producing hydrogen peroxide (Korean Patent Application Publication No. 2010-122654), wherein hydrogen peroxide may be directly obtained at high yield from oxygen and hydrogen using a catalyst having polymer electrolyte multilayers configured such that metal particles (gold, platinum, palladium, ruthenium, rhodium, iridium, silver, nickel, copper, cobalt, titanium, osmium, etc.) are attached (inserted) on a carrier (support), in the presence of a reaction solvent without the addition of an acid promoter.
However, the above patent merely discloses the use of Pd alone as a metal component. Based on the test results of production of hydrogen peroxide for a long period of time (e.g. 1000 hr or more), when using a catalyst having polymer electrolyte multilayers containing only Pd, high hydrogen selectivity and hydrogen peroxide yield may be maintained but the hydrogen conversion may be decreased. Meanwhile, with the aim of overcoming the problems as above, attempts have been made by the present inventors to test the long-term (e.g. 1000 hr or more) reaction activity using a Pt—Pd binary metal catalyst, resulting in high hydrogen conversion and hydrogen peroxide yield but lowered hydrogen selectivity.
For the synthesis reaction of hydrogen peroxide via direct reaction of hydrogen and oxygen, there is required a catalyst able to maintain high catalytic activities (hydrogen conversion, hydrogen selectivity and hydrogen peroxide yield) for a long period of time.